The present invention relates to wheel suspension assemblies for vehicles, and more particularly, to a suspension assembly which limits torquing stresses caused by the vertical and rotational movement of the axle beam against the suspension bracket on the vehicle chassis as the wheel moves vertically or rotationally.
Vehicles for off road driving generally have a chassis, which includes a pair of spaced apart longitudinal chassis members, a center cross member, transversely interconnected between the longitudinal chassis members at a point near their mid regions, and a suspension cross member between the longitudinal chassis members near an end of the longitudinal chassis members. The longitudinal chassis members each have a front end which curves upwardly to extend over the vehicle's axles and various other suspension members. Each of the longitudinal chassis members has a suspension connection location for each wheel suspension, a spring attachment adjacent to the wheel and the radius arm attachment rearward of the wheel. Conventionally, two wheel suspension assemblies are mounted at the front of the vehicle, one on each side. Each has an axle beam extending across the front of the vehicle with an outboard end on which a spindle is attached for rotationally mounting a wheel, and an inboard end coupled to a suspension cross member at a predefined downwardly projecting location. The suspension assembly also includes a radius arm having a forward end coupled adjacent to the outboard end of the axle beam, and a rear end pivotally mounted to a chassis suspension connection location.
As the vehicle as driven over bumps and holes in the road, the wheel moves vertically forcing the axle beam to pivot about a primary axis on the axle beam and forcing the rear end of the radius arm to pivot about a second axis generally perpendicular to the primary axis. This movement of the radius arm maintains the spindle end of the axle beam at a fixed distance from both the suspension connection location and the predefined downwardly projecting location on the suspension cross member. Thus, the spindle end of the axle beam will move along an accurate path as the radius arm and axle beam pivot about their connection points on the longitudinal chassis member and suspension cross member, respectively. However, pivotal movement of the axle beam as the spindle rotates through the arc results in torquing of the axle beam at the point the axle beam is pivotally attached to the suspension cross member, bending of the radius arm at the point the radius arm is attached to the longitudinal chassis member, and transmission of this bending movement into the longitudinal chassis member. This movement further results in the application of shear stresses to the entire suspension assembly. Conventionally, the radius arm is attached to the longitudinal chassis member at a location near the wheel and spindle, where the longitudinal chassis member has been bent upwardly to project and extend over the components of the suspension assembly. However, connection of the radius arm on this raised, near position of the longitudinal chassis member has been found to cause extreme torquing and shearing stresses to be exerted against the suspension bracket and the suspension cross member, and through the radius arm against the longitudinal chassis member. Such extreme stresses have been found to cause failure of the suspension bracket and stress fractures in the suspension cross member, the axle beam, the longitudinal chassis member, and the radius arm. Such structural failures can cause the vehicle to become highly unstable and dangerous to operate.
Further, torquing of the axle beam against the suspension bracket and radius arm against the longitudinal chassis member causes a binding effect on the wheel as it travels vertically in response to road hazards. This decreases the reaction time of the wheel, that is, the time it takes the wheel to recover after encountering a road hazard and resume its normal position, resulting in a rougher "ride." This binding also causes a springing action resulting in increased "wheel rate" also referred to as an increased ride frequency.
Additionally, the movement of the wheel about an arcuate path as the radius arm pivots about its pivotal connection point to the longitudinal chassis member causes the caster angle to change, resulting in changes in vehicle response and control.
Consequently, there is a need for an improved suspension assembly for off-road vehicles which will allow large vertical movement of the wheel without exerting excessive stresses against the various suspension assembly members, minimizing undesirable vibration and providing a smoother, more comfortable and softer ride.
The present invention solves these problems by providing a suspension assembly for each of one or more wheels, where the radius arm has been lengthened to interconnect to the longitudinal chassis member at a lower location proximate to the center cross member which is rearward of the upward bend of the longitudinal chassis member which extends over the other members of the suspension assembly. The new connection point is therefore below the previous connection point for the radius arm and along the longitudinal chassis member so that forces transferred through the radius arm to the longitudinal chassis member are primarily longitudinally, rather than transversely, transferred thereby greatly reducing the shear stress component of the force. Furthermore, by lengthening the radius arm, the angle of rotation of the axle beam is greatly reduced, causing the torquing of the axle beam against the suspension bracket, axle beam itself, suspension cross member, radius arm, radius arm bracket, and longitudinal chassis member to be greatly reduced. To further eliminate torquing stresses against the suspension cross member, a modified suspension bracket is also provided to be mounted to several surfaces of the suspension cross member oriented in different planes.